Beta cell transplantation holds great promise to improve treatment of Type 1 diabetes but a number of obstacles need to be overcome first. Among these is the scarcity of available donor islets. Embryonic stem (ES) cell derived beta cells can in principle supply unlimited numbers of beta cells for transplantation but reliable protocols for generating fully functional beta cells are not yet developed. Formation of definitive endoderm (DE) cells from embryonic stem cells has been reported for both mouse and human ES cells in e.g. WO 2005/116073, WO 2005/063971 and US 2006/0148081. Efficient generation of pancreatic endoderm (PE) cells from e.g. DE cells is advantageous for generation of insulin-producing beta cells for the treatment of diabetes.
In attempting to cultivate adult pancreatic islet cells, the objective has long been to isolate pancreatic and pancreatic endocrine progenitor cells that are capable of differentiating into pancreatic beta cells or Islets. One important step in isolation of pancreatic endocrine progenitor cells would be to identify recognizable cell markers, specific for the pancreatic endocrine progenitor cells. In some aspects one important step in isolation of the pancreatic endocrine lineage from the acinar lineage would be to identify recognizable cell markers, specific for the pancreatic ductal/endocrine cells, pancreatic endocrine progenitor cells and pancreatic early endocrine cells. Both intracellular and extracellular markers have been investigated for this purpose. Intracellular markers, particularly those from embryonic cells that develop into mature islet cells, have been extensively studied as progenitor markers. In some aspects these intracellular markers are transcription factors detected in embryonic pancreatic cells that develop into mature islet cells. Transcription factors such as Pdx1, Ngn3, Pax6, and Isl-1, for example, have been studied. They are expressed in cells that are programmed during embryonic development to become pancreatic endocrine cells. However, these intra-cellular markers offer less practical value than extracellular markers, because analysis of expression of those markers requires either the killing of the cells or permanent modification of the cells by genetic engineering of reporter genes into the cells.
Once identified, extracellular markers would offer the advantage that the cells expressing the marker can be sorted under sterile conditions and kept alive. Epithelial cell adhesion molecules such as Ep-CAM and integrins have been investigated as pancreatic islet progenitor markers. See e.g., Cirulli et al., J. Cell Biol. 140: 1519-1534 (1998); and Cirulli et al., J. Cell Biol. 150: 1445-1460 (2000).